1. Field of the Invention
The present invention relates to a disc reproduction apparatus capable of reproducing a data from a disc-shaped recording medium and in particular to reproducing a main data and a bar code data from the disc.
2. Description of the Prior Art
As an optical disc recording medium, a CD (compact disc) has been widely spread in various fields including music. The CD for music is normally a reproduction-dedicated medium, but a writable disc is also developed which is called CD-R (compact disc recordable).
On the other hand, a disc called DVD (digital versatile disc/digital video disc) is also developed as an optical disc recording medium which can preferably be used for multimedia application. The DVD is suggested to be used in a wide range of fields including a video data, audio data, computer data, and the like. Although the DVD has a size identical to the CD (with diameter of 12 cm), its recording capacity is remarkably increased by a reduced pitch of the recording track and the data compression technique.
This DVD has been suggested to be used as a reproduction-dedicated DVD-ROM, a DVD-R into which a data can be written once, and a DVD-RAM which can be re-written as many times as desired.
Moreover, in the development of these types of DVD, there has been suggested that each disc be provided with a BCA (Burst Cutting Area) as an area for recording a data which identifies the individual disc.
A code (signal) to be recorded in this BCA is recorded by using a YGA laser apparatus to eliminate an aluminium deposited surface, after a predetermined main data such as a video data is recorded in a disc which is a DVD-ROM for example. Consequently, the BCA code is recorded only on one side of the DVD-ROM.
As shown in FIG. 1, this BCA code consists of stripes of a bar code shape arranged in a circumferential direction of the disc, each stripe extending about k1 mm at 22.3 (+0/-0.05) mm to 23.50 (.+-.0.05) mm from the center of the center hole. In this BCA, a code is recorded by the RZ modulation method and can be read out by an optical pickup of disc reproduction apparatus.
The operation related to reading of the bar code data from this BCA is a simple one in a disc system of the CAV method (rotation at a constant angular velocity).
That is, while a disc is rotated at a constant angular velocity, the optical pickup obtains a reflected light information from the BCA and from this reflected light information is obtained a pulse signal whose level at each moment is determined at a clock timing synchronized with the disc rotation.
For example, FIG. 2A shows an example of a bar code data and FIG. 2B shows an electrical signal pulse obtained from a reflected light from this bar code data. The level of this pulse is determined with a clock synchronized with the disc rotation as shown in FIG. 2C so that a data of "1" and "0" can be extracted according to the bar code data as shown at the bottom of FIG. 2C. By decoding the data string consisting of the extracted "1" and "0", it is possible to obtain the contents of the disc individual information recorded as the bar code data.
However, in a disc system of the CLV method (rotation with a constant linear velocity), it is impossible to carry out rotation of an accurate angular velocity and it is impossible to realize the bar code data reading method as shown in FIG. 2.
To cope with this, it is necessary to provide a mechanism and a circuit for controlling a constant angular velocity only for read out of the BCA.
However, addition of a CAV control system besides the CLV control system brings about a complicated circuit and mechanism, increase of the apparatus size, and increase of productions costs, accordingly it is desired to provide a technique which enables to preferably read out a bar code data without strictly controlling the angular velocity of the disc rotation.